Kondo effect in a quantum critical ferromagnet

TL;DR

This paper investigates the Kondo effect in a quantum critical ferromagnetic spin chain with an impurity, revealing impurity screening, specific heat behavior, and critical phenomena through Bethe ansatz analysis.

Contribution

It provides a detailed Bethe ansatz solution showing impurity screening and specific heat scaling in a quantum critical ferromagnet, a novel insight into impurity effects at criticality.

Findings

Impurity acts as a diamagnetic center for J>0.

Local specific heat scales as T^{3/2}.

Impurity locks into bulk critical behavior for J<0.

Abstract

We study the Heisenberg ferromagnetic spin chain coupled with a boundary impurity. Via Bethe ansatz solution, it is found that (i) for J>0, the impurity spin behaves as a diamagnetic center and is completely screened by 2S bulk spins in the ground state, no matter how large the impurity spin is; (ii) The specific heat of the local composite (impurity plus 2S bulk spins which form bound state with it) shows a simple power law $C_{loc}\sim T^{3/2}$. (iii)For J<0, the impurity is locked into the critical behavior of the bulk. Possible phenomena in higher dimensions are discussed.